A wireless communication system has been extensively developed to provide various types of communication services such as audio, data, etc. In general, the wireless communication system is a multiple access system capable of supporting communication with multiple users by sharing available system resources (bandwidth, transmission power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, a multi-carrier frequency division multiple access (MC-FDMA) system, etc.
Device-to-device (D2D) communication refers to a communication scheme in which audio, data, etc. are directly exchanged between user equipments (UEs) without passing through a base station (evolved NodeB (eNB)) by configuring a direct link between the UEs. D2D communication may include a scheme such as UE-to-UE communication, peer-to-peer communication, etc. In addition, the D2D communication scheme may be applied to machine-to-machine (M2M) communication, machine type communication (MTC), etc.
D2D communication is considered as a scheme capable of relieving a burden on a base station resulting from rapidly increasing data traffic. For example, according to D2D communication, network overload may be reduced since data is exchanged between devices without passing through a base station unlike a conventional wireless communication system. In addition, when D2D communication is introduced, it is possible to achieve effects such as a reduction in procedures of a base station, a reduction in power consumption of devices participating in D2D communication, an increase in data transfer rate, an increase in network capacity, load balancing, extension of cell coverage, etc.